Power Supplies

Discussion in 'Hardware' started by gamerdude1989, Mar 22, 2011.

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  1. gamerdude1989

    gamerdude1989 Banned

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    Hi guys.
    Right two questions that are related, that im not sure about.

    1. As there are many different power PSU's ie: 550w, 1000w etc.
    I know you have to get one that can power the mobo etc.
    if your mobo requires 350w, you need a higher W psu etc.
    But say i got a 500w psu, and my mobo requires 350w and my graphics card requires 250w, that equals 600w. would the psu not power it correctly?
    or does it not take away Whattage like how i just explained it?

    and

    2. say a 1000w psu, thats 1Kw of electric per hour? surely that would cost alot to run a pc?

    thanks
     
  2. Cosmo_1847

    Cosmo_1847 Kiss of death

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    Power supply ratings are the peak continuous rating. That is a 1Kw PSU can supply 1Kw of power. If you have a 200W computer with a 1Kw PSU that will use 200W of power. It should also be pointed out that commonants are rated as their peak wattage. A graphics card may use 200W but only 100W when idle. This means that your computer should run but when performace is required it falls over.

    If you have a 600W computer with a 500W supply then variety things could happen, the best being a BSOD or the computer suddenly powering off. The worse case is that there is a loud bang and things never turn on again. I'd imagine it would be like blowing a fuse. My cluster idles at 650W and peaks at 1150W, so if it idles on a 3 amp fuse it will blow when performace is required.

    PS I moved the thread to hardware.
     
  3. latency

    latency Existentialist

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    First we need to understand three facts:

    1. PC PSUs are very over rated. Most components don't use nearly as much as people think.

    2. The computer can use as little as 50% of it's load power when idle, and it's rare for ALL components to be loaded at the same time.

    3. Cheap PSUs may not deliver their rated wattage. My estimates assume a trustworthy brand.

    Bottom line, average PC like mine, with a respectable spec, but nothing exotic like two or more hard drives, GPUs, etc, uses 350watts tops, including overclocks. I've tested that with a power meter.
    I run a 430w PSU, which easily copes.

    General guide:

    CPU: 100w
    GPU: 100w
    Mobo: 40w
    Hard drive: 15w
    Optical drive 15w
    RAM: 10w
    Fans/lights: 15w
    Misc overheads / margin for error: 20w
    Overclock: Varies.

    +50w to PSU final figure to allow for PSU efficiency and to avoid keeping it at load all the time.

    Based on a PC like mine, even with twin graphics cards and an extra hard drive, I can still run a 550w PSU.

    So basically, unless you've got some very exotic hardware, anything over 600 is overkill.


    Now to answer your questions:

    1. When hardware says 'requires 350w PSU' or a graphics card says 'requires 500w' etc, this doesn't mean the component uses that much power, it's a HUGE generalisation that accounts for the rest of the system as well.
    When, say, AMD say their GPU needs 550w, they're assuming you're going to have a respectable CPU, couple of HDDs, and so on, as well, and they estimate with that in mind.
    In other words, these sys requirements are tosh. Calculate your own power consumption, or pay £20 for a plugin energy meter from maplins and that'll tell you actual power usage.

    2. Assuming full load, a 1000w PSU (1Kw) will indeed use 1 kilowatt-hour of electricity, per hour. That's a lot for something that's on for a period of time.

    However, as per my previous notes, a computer, even with a 1Kw PSU, will likely be using significantly less. Assuming I've got a game running ALL THE TIME, my computer consumes 320w (~1Kwh every 3 hours).
    At idle, the consumption falls to just under 200w on my system.

    Even with that modest consumption, as you can see, it ain't cheap to leave your computer on, which is why I scorn people who chase up-time figures.

    My server is a MacMini, which idles at about 60w. A laptop can easily run as a small home server, and that'll idle at 40w tops.

    To put all this in perspective, typical electric costs are about 9p per Kwh on a reasonable rate. So if your computer loads at 400watts, and you play games for 5 hours a day (1Kwh every 2.5hours), it'll cost £5.58 a month to run your computer.

    If you leave your computer idling at 200watts for the rest of the day, that's £19.53.

    In sleep mode, a PC uses about 5w, but considering that most computers can start up within a couple of minutes, it's hardly a big deal to turn it off entirely.

    Everyone do the world a favour- turn off your PC when you're not using it ;)
     
  4. gamerdude1989

    gamerdude1989 Banned

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    ah dude your a star.
    That cleared up so much for me.

    Well im thinking about running something like 550w PSU.
    Im just waiting on some things to sell on ebay then i will be ordering my new hardware.
    So i am thinking ahead of hat PSU to buy,

    The current PSU in my pc is 350w max.
    (i know junk specs), but its running
    MSI mobo
    P4 2.8 cpu
    Ati radeon gpu
    ram obviously
    optical drive
    1 hdd, (did have 3)
    cathode kit
    1x front induction, 1x rear, and 1x side fan, aswell as cpu heatsink fan.
    and it seams to run fine.

    thanks
     
  5. latency

    latency Existentialist

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    Bear in mind I'm making some generalisations of my own there- for example, you may have a lower electric rate during night hours (my shop's night rate is something like 6.9p), so my running costs represent worst case figures.

    But the value of saving electricity is under rated.

    I'm not a tree hugger, I don't care about global warming- I just want to pay less on my utility bills ;)

    It's amazing how much you can save by understanding the electric consumption of all sorts of things including your computer.

    Hell, I turn my microwave off at the socket, because it uses 10 watts just to have the 0:00 displayed on the front when I'm not using it.
     
  6. gamerdude1989

    gamerdude1989 Banned

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    Yeah i agree, i dont care about the global warming, a few people doing things to help isnt going to stop the other millions of people that dont care.
    I always turn plugs off, every one in the house apart from fridge and freezer, simply because i was in a house fire when i was younger down to fault electrics. lol

    I simply want lower electric bills lol as we have just recieved a bill of 730quid for 6 months (no faults of incorrect readings)

    so to recap.
    i have a 550w psu, so say if my pc only sucks up 350max, then my psu wont be constantly drawing 550w? it will only use 300w of electric? coz 550w constantly can equal alot when my pc is turned on the minute i get up in the morning and only gets turned off the minute i go to bed at night.
    it wouldnt seam so bad if it was the case about the 300w statement i asked above.

    thanks
     
  7. Cosmo_1847

    Cosmo_1847 Kiss of death

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    The computer, like any other device, will only draw the power required at the time. For example my laptop has a 100w power supply. It uses about 40w full load and about 70w ish when under full load and charging. If your computer requires 350w to run then that is what it will pull even if the power supply is greater than 350w. PSUs are more efficent and higher loads so it would be more efficent to have a 500w PSU rather than a 1Kw PSU for a 350w load.
     
  8. Digital Doctor

    Digital Doctor Loving AMD's new AM1 CPU

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    Ahh the PSU, the most important part of the system even though some dont think so. Good internal components in a PSU count for everything, IE an antec 400w psu will do a better job than a cheap 550w one, for graphics cards its the amperage thats more important.

    Its better to have a higher rated psu as then you will have a "safety margin" also future upgrade room.
     
  9. reaper

    reaper .....of the grim variety!

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    I like to think of the PSU as the "heart" of the machine.

    Can have the finest components in the world, but without a decent "heart" beating away to power it all, you are wasting your time!

    :p
     
  10. latency

    latency Existentialist

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    Quoted For Truth.


    The amperage is definitely the way to spot the stronger PSUs... the fakers with a big sticker wattage but no grunt can be spotted by the low amps as you say.

    But the amps can be difficult to read sometimes, because PSUs deliver the amps in different ways. There are single, twin, and triple rail PSUs on the market, dividing up the power- and of course some PSUs will weight their amps on the 5 and 12 rails, and leave a weaker 3.3v rail, which is the one powering RAM.

    Bottom line again, stick to trusted brands.
     
  11. gamerdude1989

    gamerdude1989 Banned

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    hi guys, thought id ask a quick question on my old topic :D

    As Digi Doc states, for Gfx cards, Amperage is more important.
    Since im waiting for my xfx geforce 5870 1gb to be delivered, im also buying a new PSU, just to give the better power, and extra headroom.

    Im not sure exactly what brand im going for yet, But wanted to clarify things a little before i decide.

    OK, as Latency said, 600w should be about all i need.
    To be honest, im wanting a little more headroom, just incase of extra power suckers that happen to install into my case in the future.

    So im going for a 750w

    What exactly does the term, "rails" mean, i understand the more amount is better, but what are they? and whats the difference between a twin rail and a quad rail?

    secondly, as Amperage for the gfx is more important. looking around, just browsing through different PSU's, it says " +12v1 32A, +12v2 32A. Im guessing the "+12v1, 2, 3 etc" are meaning Rails??? and is 32A good?

    Im just wanting to know for sure, so i can just get one decent PSU and be done with it.

    Thanks
     
  12. Digital Doctor

    Digital Doctor Loving AMD's new AM1 CPU

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    Latency can you explain im too tired.
     
  13. gamerdude1989

    gamerdude1989 Banned

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    Anyone?
     
  14. latency

    latency Existentialist

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    Here's a breakdown of your system- wattages are estimates, but not going to be more than 10w under actual.

    Mobo - 40w
    CPU - 95w
    RAM - 15w
    HDD - 20w
    Graphics - 100w
    Fans and other stuff - 20w
    Random made up over heads - 50w

    = 340watts Load.

    Still think you need 750watts?

    A voltage rail is a voltage supplier from the input 240v.

    In a single 12v rail PSU, all 12v power eventually connects back to a single point in the PSU- on a modern system, that's a lot of wattage to a single point.

    A twin-12vrail PSU will have two 12v points from the 240v input, so they share the total 12v load.

    And so on...

    Based on my previous statement, you'd imagine more rails = better.
    But as you can see, PSUs with 4 rails tend to have much lower amperage per rail.
    This suits a system with many objects in it (like a lot of hard drives), but it doesn't suit a system with single high-load devices (like graphics cards), because it's hard to load-share big load devices.

    Generally though, two or four rails are just fine.

    32amps * 12v = 384watts max load on the 12v rail- allowing for the fact that a lot of devices like the RAM, mobo components, HDDs use power from the 5v and 3.3v rails, this is plenty.

    The two big loads on the 12v rails you need to worry about are the CPU and graphics card, and these rarely add up to more than 250watts.

    Generally, the amperages on any decent brand PSU will be allocated sensibly.

    The only thing you really need to worry about is the brand- it means everything in PSUs, and if you're planning on buying a Overclockers UK own-brand PSU, I'd jog on, because that could be anything.

    Buy a Corsair, OCZ, Targan or Seasonic, because you can't go wrong with those brands.

    Corsair and OCZ are built by Seasonic I think, but they're great power supplies.

    My Corsair 430w cost me about £40 and powers my system with ease. Granted you'll want a bit more head room than 430w (I can't power two graphics cards with this PSU), but the point stands.
     
  15. gamerdude1989

    gamerdude1989 Banned

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    thanks for that latency.

    Hmm i wish i could of bought a "top" PSU, but unfortunately ive drained my money on the 5870. But aslong as it powers fine for now, then i guess i could upgrade again in the near future.

    the one i have bought is Quad Rail with 32A Per Rail.

    Hope fully that will do nicely for now.

    Thanks
     
  16. gamerdude1989

    gamerdude1989 Banned

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    My mate (who was building the file server), has given me his pc, so that i can build it into a file server for my home (mainly so that my mrs can store her crap on it to get rid of the horrible slowness of her netbook).

    I was mistaken, i thought the psu was 450w, its not, its 300w, He give me the pc due to the fact that it wont power up, So i thought id check the simple things first.
    The mains plug.. only has a 3A fuse in it
    What fuse are they meant to have?
    I thought all PC's power from 13A fuse in the plug?

    thanks
     
  17. brumster

    brumster Midland Muppet

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    A 300w power supply should be fine on a 3 amp fuse - 3 amps at 240v is 720 watts.

    13 amps is over 3kw - pretty serious power consumption for anything; that's more like cooker or kettle territory!
     
  18. latency

    latency Existentialist

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    3A fuse will blow at 720watts.

    A little low for a PC, but not going to cause a problem with a 300w PSU.

    Kettle lead is hardly a rare cable though, you can test that in seconds.
     
  19. gamerdude1989

    gamerdude1989 Banned

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    would someone please explain how you work out what fuse is needed in certain things?

    isnt it.

    W divided by V = Amps?

    so 300w psu in uk 220v = 1.36A.

    So my psu will only suck up 1.36A, so a 3A fuse is fine, which allows for fluctuations?

    am i correct?
     
  20. brumster

    brumster Midland Muppet

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    Ahh, GCSE physics comes back to me :)

    Yes, you're spot on...

    P = I x V

    Next week we'll do bridge rectifiers ;)